<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>显示层|级</title>
    <style>
        #d1{
            width: 200px;
            height: 100px;
            background-color: red;
            position: absolute;
            z-index: 1;
        }
        #d2{
            width: 100px;
            height: 200px;
            background-color: blue;
            position: absolute;
            z-index: 2;/*默认是0*/
            float: left;
            left: 108px;
        }
        #d3{
            width: 100px;
            height: 200px;
            background-color: green;
            position: absolute;
            z-index: 0;/*默认是0*/
        }
    </style>
</head>
<body>
    <div id="d1"></div>
    <div id="d2"></div>
    <div id="d3"></div>
</body>
</html>